1. Technical Field of the Invention
The present invention relates to a generation control apparatus for vehicles, which controls the condition of power generation of a vehicle generator loaded on such vehicles as passenger cars and trucks.
2. Related Art
Generally, vehicle generators are configured to detect the voltage of a control terminal (which is the positive terminal of a battery or the output terminal of the vehicle generator) for comparison with a reference value. As a result of the comparison, when the voltage of the control terminal is higher than the reference value, a transistor for performing on/off control of the field current is turned off. On the other hand, when the voltage of the control terminal is lower than the reference value, the transistor is turned on. Thus, such a vehicle generator is configured to control the duty factor of the field winding to keep the voltage of the control terminal at a constant level.
When an electrical load is applied, an amount of current corresponding to the applied electrical load is taken from the battery. Then, control is performed for an amount of voltage reduction corresponding to the taken out current, by increasing the duty factor of the field winding to increase the electric power generation, so that the voltage of the control terminal is regulated. Since this control is instantaneously performed, the voltage of the control terminal is hardly reduced but kept at a substantially constant value. However, this control necessitates a sharp increase of the field current of the vehicle generator, which leads to a sharp increase of the power generation torque of the vehicle generator. As a result, the engine speed is reduced. In particular, in an idling speed region, the reduction in the engine speed can cause engine stall.
A technique for taking a measure for the above problem is disclosed, for example, in Japanese Unexamined Patent Application Publication No. 5-300669. In this technique, a limitation is imposed on the increase rate of the duty factor of the field winding, in a case where the field current is increased, to suppress the sharp increase of the power generation torque of the vehicle generator. This technique lies in the function of suppressing the power generation of the vehicle generator. Accordingly, although torque fluctuation can be suppressed by this function, power generation will be insufficient while this function is exerted. Resultantly, the output voltage of the vehicle generator will be reduced.
In the technique disclosed in Japanese Unexamined Patent Application Publication No. 5-300669, the reduction in the output voltage is induced by imposing a limitation on the increase rate of the duty factor of the field winding at the time of applying electrical load. Accordingly, it has also been a problem that, when headlamps are lit, the intensity of light of the headlamps can vary.
In addition, electronic devices, including ECUs (electronic control units) and EPS (electronic power steering) sensitive to variation of voltage, are increasingly loaded on vehicles recently. Thus, in order to ensure normal operation of such electronic devices as well, engine stall is required to be prevented, while the voltage is prevented from being extremely reduced.